High voltage supply circuit for television systems



Nov, 7, 1939.

Filed Dec.

R. B. DOME HIGH VOLTAGE SUPPLY CIRCUIT FOR TELEVISION SYSTEMS spa Inventor-:

Robert, B. Dome Patented Nov. 7, 1939 HIGH VOLTAGE SUPPLY CIRCUIT FOR TELEVISION SYSTEMS Robert B. Dome, Bridgeport, Comm, assignor to General Electric Company, a corporation of New York Application December 14, 1938, Serial No. 245,690

Claims.

My invention relates to high voltage power supply circuits and particularly to power supply circuits for cathode-ray tubes used in television sys- I plifier or other tubes of the system. The above arrangement, suggested heretofore, entails the disadvantages that this special winding is of relatively high cost.

It is .an object of my invention. to provide a high voltagepower circuit for television cathode= ray tubes which adds relatively little to the cost of the system.

It is a further object of the invention to utilize as a voltage source for the cathode-ray tube the secondary winding of the power transformer which supplies the usual amplifier or other tubes of the receiver.

It is another object of the invention to provide, for the energizing of the cathode-ray tube, a voltage which is the sum of the voltage produced by a secondary winding of the power transformer and the voltage, including that due to the drop through a filter reactor, supplied to a circuit connected to the power transformer for the supply of power to the amplifier or other tubes of the system.

It is a still further object to provide alow cost filter system for the high voltage cathode-ray tube supply circuit.

The novel features which arecharacteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advan tages may best be understood by reference to the following description taken in connection with the accompanying drawing, the single figure of which is a diagrammatic representation of a portion of a television receiver in which my invention has been embodied.

In the singlefigure of the drawing the television system illustrated therein is similar in general to the television system illustrated in my above mentioned prior application, Serial No. 237,785. The present system includes a usual rectifier circuit for the supply of power for the operation of (Cl. I'll-$7) conventional radio receiver tubes. This usual supply circuit, designated generally by S1, comprises a transformer I0 having a primary H connected to a current source (not shown) and a secondary l2; a rectifier apparatus or tube i3 5 having anodes M and [5 connected to the opposite terminals it and I l of secondary I 2 and a cathode i8 supplied with heating current from a secondary winding IQ of transformer it; output terminals 20 and 2H connected respectively to the 10 cathode it and to the mid-tap 22 of secondary i2; and a filter means including a filter reactor 23 and capacitors 24 and 25.

In the television system illustrated in the above mentioned prior application, in order to provide 15 the high unidirectional voltage required for the cathode-ray tube (not shown) and which is to be supplied thereto through the output terminals 26 and 217 of the cathode-ray tube supply circuit designated generally by S2, the relatively high 20 voltage secondary winding i2 is utilized as part of the voltage source, this secondary 82 being already provided on transformer it and being designed for the supply of voltage for the conventional radio receiver tubes (not shown), or for 25 other purposes, through the output terminals 253 and 20. It has been found, however, that the voltage supplied by my above-mentioned system utilizing secondary l 2 as part of the cathoderay tube voltage source is insuflicient for the effl- 30 cient operation of a certain cathode-ray tube which is larger than the tube for which the prior system was designed. In accordance with my present invention I have provided the additional voltage required for the larger tube, while at 35 the same time retaining secondary 92 as part of the voltage source for this tube, by extending one end of secondary 82, additional turns 28 being providedto obtain this additional voltage. For the purpose of utilizing the total secondary wind- 40 ing 29, thus constituted by the original secondary i2 and the additional winding 28, as a part of the voltage source for the cathode-ray tube supply circuit, an auxiliary rectifier tube 30 is provided,

as in my above-mentioned prior system, having 5 an anode 3| and a cathode 32 heated from a secondary winding 33 on transformer I0. Rectifier 30 is then supplied with alternating voltage from the total secondary winding 29 through a capaci-v tor 34 connected between one terminal 35 of the 5 winding 29 and the cathode 32 of the tube 30, and through a capacitor 36 connected between the other terminal l6 of the winding 29 and the anode 3| of the tube 30. Cathode 32 of auxiliary rectifier 30 is connected to the high voltage terminal 26 of the cathode-ray tube supply circuit through a connection including a resistor 31. The anode 3| of tube 30 is connected, as in the abovementioned prior system, through a resistor 38 to the connection 39 between cathode l8 of tube l3 and filter reactor 23, the latter reactor and the output terminals of circuit S1 thus being included in the cathode-ray tube circuit S2. A voltage divider 40 is preferably provided connected between the cathode-ray tube supply circuit output terminals 26 and 21 to permit the obtaining of additional voltages as for focus voltage for the cathode-ray tube.

Filter means for the cathode-ray tube circuit S2 comprise a filter capacitor 4| connected between output terminal 26 of the cathode-ray tube supply circuit S2 and output terminal 2|! of supply circuit S1; the resistor 31 in series with the ca pacitor 34; and a resistor 42 in series with a capacitor 43. Capacitor 34 and resistor 31 are connected in series between terminal 35 of the total secondary winding 29 and terminal 26 of circuit S2. Resistor 42 and capacitor 43 are connected in series between terminal N5 of the total secondary winding 29 and the terminal 26. The ratio of the resistance value of resistor 31 to the resistance value of resistor 42 is made substantially equal to the ratio of the alternating voltage from terminal 35 of total secondary winding 29 to tap 22, which is at ground, to the alternating voltage from terminal IE to tap 22 or ground. Preferably the ratio of the reactance value of capacitor 34 to the reactance value of capacitor 43 is also made substantially equal to the above-mentioned ratio of the alternating voltage from terminal 35 to tap 22 or ground to the alternating voltage from terminal IE to tap 22 or ground. Such ad- J'ustment of the reactance values of capacitors 34 and 43 may or may not be necessary, depending upon the degree of accuracy required in balancing out undesired oscillations.

From the foregoing description of the system illustrated in the drawing it will be seen that the radio receiver tube supply circuit S1 may be traced from positive terminal 20, through reactor 23, main rectifier tube |3, secondary winding l2 of transformer l0, and mid-tap 22 of secondary l2 to terminal 2| which is preferably at ground. It will also be seen that the cathoderay tube supply circuit S2 may be traced from the high voltage terminal 26, through resistor 31, auxiliary rectifier tube 39, resistor 38, filter reactor 23 of circuit S1, and the load between terminals 20 and 2| of circuit S1, to terminal 21.

In operation of the system illustrated in the drawing, let it be 3851111182 that the cathode-ray tube supply circuit S2 is under no-load conditions, no current being drawn from the output terminal 26, and that the supply circuit S1- is under load conditions. Under these conditions twice the RMS voltage per anode for the main rectifier |3 exists across the secondary winding I2 of transformer l0. But since in accordance with my present invention the total secondary winding 29, which is connected across the auxiliary rectifier 30, comprises the winding l2 and in addition the winding 28 which is an extension of winding 2 at one extremity thereof, therefore the total alternating voltage which is rectified by the auxiliary rectifier 30 is the sum of twice the RMS voltage per anode of main rectifier plus the voltage due to the added winding 28. Also, under the assumed load conditions in circuit S1 a predetermined unidirectional output voltage exists across terminals 20 an of 011,-

cuit S1, and a predetermined unidirectional voltage drop due to the current drain in the supply circuit S1 exists across the filter reactor 23. A total predetermined unidirectional voltage therefore exists across the capacitor 24 of circuit S1 which is the sum of the load voltage across terminals 20 and 2| and the voltage drop across the filter reactor 23. 4

Since the anode 3| of auxiliary rectifier 30 is connected, through resistor 38 and connection 39, to the positive terminal 44 of filter reactor 23, therefore the above-noted sum of unidirectional voltages across capacitor 24 of circuit S1 is added to the unidirectional voltage produced, by rectification in auxiliary rectifier 30, from the total secondary winding 29 of transformer l0 constituted by the secondary I2, which supplies circuit Si, and the added winding 28. Therefore under the assumed no-load conditions in cathode-ray tube supply circuit S2 and load conditions in receiver tube supply circuit S1, the

total unidirectional voltage appearing across terminals 26 and 21 of cathode-ray tube supply circuit S2 is the sum of J2 times the RMS voltage across the secondary |2 which supplies the receiver supply circuit S1 plus the RMS voltage across the winding 28 added to winding |2 to produce the total excit ing secondary winding 29 which is connected across the auxiliary rectifier 30, plus the load voltage across the terminals 20 and 2| of circuit S1, plus the voltage drop through filter reactor 23 of circuit S1.

Under load conditions in circuit S2, the relatively small current in this circuit flows through resistors 31 and 38. A certain voltage drop therefore exists in these resistors. The above-noted total no-load voltage impressed across terminals 26 and 21 of circuit S2 is of such value and the voltage drop due to the resistance introduced in the circuit S2 by the resistors 31 and 38 is of such value that under load conditions in circuit S2 the resultant voltage which is supplied to the cathode-ray tube is of a predetermined desired value.

The hereinabove-described filter means for the cathode-ray tube supply circuit S2 constitute together with the winding 29, which energizes the auxiliary rectifier 30, a partial bridge circuit. Two adjacent arms of the bridge are constituted, respectively,'by the section of winding 29 between terminal l6 and tap point 22, and by the section between terminal 35 and tap point 22. The other pair of bridge arms are consti-.

tuted, respectively, by capacitor 34 and resistor 31 in series between winding terminal 35 and terminal 26 of circuit S2, and capacitor 43 and resistor 42 in series between winding terminal I 6 and the terminal 26. The load circuit from which the undesired oscillations are to be filtered is constituted by cathode-ray tube supply circuit S2, which is connected across the bridge corners constituted by the tap 22 of winding 29 and the terminal 26 of circuit S2. The filter capacitor 4| and filter capacitor 25, which are in series connection, are connected in shunt with the cathode-ray tube supply circuit S2, between the corner 22 and corner 26 of the bridge.

In operation of this partialbridge circuit the alternating voltages across filter capacitor 4| come from two sources, one from the terminal 35 of winding 29 through capacitor 34 and resistor 31, and the other from terminal I6 of winding 29 through capacitor 43 and resistor 42. These two voltages are in opposition, and the ratio of the voltage in arm 22, to that in arm 22, I6 is equal to the ratio of the resistance of resistor 31 to the resistance of resistor 42, and preferably also to the ratio of the reactance of capacitor 34 to the reactance of capacitor 43. Therefore, because of the resulting balancing of opposed voltages aci'oss filter capacitor 4| only a small ripple voltage remains across this capacitor. Since the remaining ripple to be filtered from circuit S2 is thus small, capacitor 4| need be only of relatively small capacity.

In a practical system constructed in accordance with my present invention and designed to provide approximately 1800 volts output in cathode ray tube supply circuit S2 under load conditions in this circuit, the voltage across terminals 20 and 2| of supply circuit S1 is 265 volts and the load current drain from this circuit is 180 milliamperes. In filter reactor 23, five watts are consumed and the voltage drop thereacross is Therefore, the sum of the voltage in supply circuit S1, across capacitor 2% is 2s5+2c:293

volts.

The RIMS voltage per anode in main rectifier i3 is approximately 315 volts and therefore the RMS voltage across secondary i2 is 2 315=csu The RMS voltage added to secondary if. by the turns it which with winding l2 make up the total winding 29, is 540 volts, and the total EMS voltage across winding 29 is 1170 volts.

The rectified voltage produced by auxiliary rectifier 38 under no-load conditions in circuit S2 is The total voltage at the output terminals 28 and 2? of the cathode-ray tube supply circuit S2 under no-load conditions in the latter circuit is E=1657+293=1950 volts.

' Under load conditions in circuit S2 the output current may be approximately 500 microamperes. This current fiows through resistors SI and 38. The total resistance of these resistors in order to obtain approximately 1800 volts across terminals 26 and 21 of circuit S2 is I SOOXIO- The constants for resistance and capacitance elements employed in the foregoing fractional system in supplying the desired high voltage in the cathode-ray tube circuit S2 and in accomplishing the required degree of filtering in the latter circuit are as follows:

=300,000 ohms It will be seen that by providing, as part of the voltage supply source for the cathode-ray tube, a secondary winding 29 for transformer l0 which is constituted by the already existing high voltage secondary l2 to which is added the turns 28, a required relatively very high A. C.' voltage is obtained without entailing the considerable cost of an entirely separate secondary to produce this required A. C. voltage which is rectified by the auxiliary rectifier.

My invention has been described herein in a particular embodiment for purposes of illustration. It is to be understood, however, that the invention is susceptible of various changes and modifications and that by the appended claims I intend to cover any such modifications as come within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a current source, a load circuit, means including a rectifier and a transformer having an energizing winding connected to said rectifier to supply power to said circuit from said source, a second load circuit, a winding connected in series with said energizing winding to form with said energizing winding an energizing Winding for said transformer of a greater number of turns than said first-named energizing winding, and means including a rectifier connected in series in said second circuit and across said second-named energizing winding to supply power to said second load circuit from said source.

2. in combination, a load circuit, a rectifier, a transformer winding, means to supply a voltage to said circuit from said winding through said rectifier, a second load circuit, a second transformer winding, means to connect said second winding to said first winding to form with said first winding a transformer winding of a larger number of turns than said first-named transformer winding, a second rectifier connected across said second-named transformer winding, and means to connect said second rectifier in series with said first-named circuit, whereby the voltage supplied to said first-named circuit through said first-named rectifier is added to the voltage supplied to said second circuit through said second rectifier.

3. In combination, a load circuit having a filter reactor in series therewith, a rectifier, a transformer winding, means to supply a voltage to said circuit from said winding through said rectifier, a second load circuit, a second transformer winding, means to connect said first and second windings in series to form a transformer winding of a larger number of turns than said first named transformer winding, a second rectifier connected across said transformer winding of a larger number of turns to supply voltage therefrom to said second circuit, and means to connect said second rectifier in series with said filter reactor and said second circuit.

. 4. In combination, two load circuits, a transformer winding having a center tap, means to impress a rectified voltage from said winding on one of said circuits, a winding connected to said transformer winding to form a second transformer winding having a larger number of turns than said first transformer winding, means to impress a rectified voltage from said second transformer winding on the other of said circuits, a filter capacitor connected across said other circuit, and means to connect the opposite terminals of said second transformer winding each through a capacitor and a resistor to the high tension side of said filter capacitor, the ratio of the voltages in said second transformer winding between one of said terminals and said center tap and between the other of said terminals and said center tap being equal to the ratio of the resistance of the resistor corresponding to said one of said terminals and the resistance of the other resistor.

5. In combination, two load circuits, a transformer winding having a center tap, means to impress a rectified voltage from said winding on one of said circuits, a winding connected to said transformer winding to form a second transformer winding having a larger number of turns than said first transformer winding, means to impress a rectified voltage from said second transformer winding on the other of said circuits, a filter capacitor connected across said other circuit, and means to connect the opposite terminals of said second transformer winding each through a capacitor and a resistor to the high tension side of said filter capacitor, the ratio of the voltages in said second transformer winding between one of said terminals and said center tap and between the other of said terminals and said center being equal to the ratio of the resistance of the resistor corresponding to said one of said terminals and the resistance of the other resistor and also equal to the ratio of the reactance of the capacitor corresponding to said one of said terminals to the reactance of the capacitor corresponding to the other of said terminals.

ROBERT B. DOME. 

